1. Field of the Invention
In one aspect, this invention relates to a method to control the air pressure of an air reservoir which serves as a source of motive compressed air for an air driven device. In another aspect, this invention relates to a method of maintaining sufficient operating pressure of a pressurized air supply tank utilized in an air driven system such as a vehicle braking system. In still another aspect, this invention relates to a regulator for regulating the pressure of a pressurized vessel.
2. Prior Art
Pressurized air tanks are commonly employed in air braking systems used with heavy duty service vehicles such as trucks, trailers, trains, trackmobiles and other heavy equipment. The air tank provides a reservoir of motive air to drive the brake system and also avoids the need for simultaneous generation of motive air at the time braking is needed.
The air pressure vessel also provides an excess supply of air to overcome air losses resulting from line and other system leaks. Air leaks can be a serious problem and it is common in the train and trackmobile air brake art to dump all air which results in an emergency vehicle stop when air pressure drops below a predetermined safe operating pressure. That is, the motive air drives the air brakes to a non-braking "open" position and maintains them in a non-braking position. When low air pressure is detected, the air is dumped from the pressure vessel, the brakes engage and the vehicle is brought to a stop. This is a long standing safe operating practice.
For example, with train and trackmobile air systems, a low air pressure indication will result in an air dump, brake engagement and inactivation of remote vehicle control systems which are used to direct the vehicle from a distance. Since the pressure vessel is relatively small, it does not take much air leakage to cause a work stoppage. The air compressors generally used with trains and trackmobiles are driven off the flywheel or crankshaft of the vehicle motor and thus the air generation output is dependent upon the vehicle engine speed. At time of air loss and vehicle brake stoppage, the vehicle engine speed is generally reduced. At reduced engine speeds, air compressor drive speed is relatively slow and thus air compression and tank filling is a slow process. In some instances, we have found that repressurization of the air reservoir could take from about ten to fifteen minutes or more. This results in a significant loss of work time and vehicle utilization.
To avoid vehicle downtime and work delays, we have tried several different approaches to solve the problems associated with the air losses and automated vehicle braking. First, we tried using a remote air source. We connected, via flexible hose, high pressure air from a stationary external compressor and stationary second pressure vessel. Although our vehicle had a relatively limited travel zone along a short segment of track, we found stationary air supplies and hose connections were not practical because of the restrictions imposed on vehicle movement. We experimented also with large volume output rotary screw compressors as a substitute for gear-type compressors and found no operating improvement where the compressors were driven by the crankshaft or other drive source when the power output of which was dependent on engine speed.
Because of the lost vehicle-utilization time caused by air brake system shutdown, there is a need for improved methods of controlling pressure of pressurized tanks utilized in air driven vehicle braking systems and for improved air tank pressure regulators.